An air room is one of the factors determining frequency characteristics of a unidirectional dynamic (electromotive) microphone as is disclosed in Japanese Unexamined Patent Application Publication No. 05-049090. A hand-held microphone such as a vocal microphone typically has an air room in a cylindrical grip housing. FIG. 6 illustrates an example of such a microphone.
A hand-held unidirectional dynamic microphone includes, for example, a cylindrical grip housing 10 formed by die casting, and a microphone unit 20 supported at a first end of the grip housing 10. The microphone unit 20 incorporates a diaphragm (not shown), to which a voice coil is attached, and a magnetic generator circuit (not shown) having a magnetic gap, where the voice coil is disposed so as to vibrate with the diaphragm within the magnetic gap.
The microphone unit 20 has unidirectionality and thus includes a front acoustic terminal 20a and a rear acoustic terminal 20b. The microphone unit 20 is attached to the first end of the grip housing 10 with a coupling ring 11 therebetween while the rear end of the microphone unit is hermetically inserted in the coupling ring 11. An elastomeric shock mounting member 12 is provided between the coupling ring 11 and the grip housing 10 in order to reduce handling noise. A pressure ring 13 is also provided.
A connector storage 14 is integrally provided at a second end of the grip housing 10, and a plug assembly 30 is mounted as an output connector within the connector storage 14. The microphone unit 20 is connected to the plug assembly 30 through an undepicted lead line. The inside of the grip housing 10 is a cavity that acts as an air room 10a of the microphone unit 20.
The air room 10a preferably has a large capacity improving sound quality in a low frequency range. In any case, air should not enter the air room 10a from the outside for satisfactory directionality. The inside of the grip housing 10 has been therefore sealed at the second end having the plug assembly 30 with, for example, a silicone sealant 15 after the microphone unit 20 is connected to the plug assembly 30 through the lead line. The plug assembly 30 is inserted/extracted into/from the grip housing 10 at the first end of the grip housing 10 for assembling the dynamic microphone or replacing the plug assembly 30.
Japanese Unexamined Patent Application Publication No. 2005-277652 discloses another embodiment of a dynamic microphone having an air room in a grip housing. A special component for the air room is coupled to the rear of a microphone unit.
This unidirectional dynamic microphone includes a grip housing 100, a cavity sleeve 200, a dynamic microphone unit 20, and a plug assembly 30 as shown in FIG. 7.
The microphone unit 20 has unidirectionality and thus includes a front acoustic terminal 20a and a rear acoustic terminal 20b. In addition, the microphone unit 20 is of a dynamic type, and thus it incorporates a diaphragm (not shown), to which a voice coil is attached, and a magnetic generator circuit (not shown) having a magnetic gap, where the voice coil is disposed so as to vibrate with the diaphragm within the magnetic gap.
The plug assembly 30 is a 3-pin connector having a cylindrical base 31 including an electric insulator, through which a first ground pin (omitted in the drawing), a second pin 32 for a hot part of signals, and a third pin 33 for a cold part thereof penetrate. The connector further includes a screw 34 that moves in a radial direction of the base 31 and a ground terminal plate 35 having an internal thread for the screw 34, where the ground terminal plate 35 is electrically conducted to the first ground pin through an undepicted fitting.
The microphone unit 20 and the plug assembly 30 are attached to the cavity sleeve 200. The cavity sleeve 200 has a cylindrical shape formed by die casting, where the inside of the cavity is used as an air room 201 as a part of an acoustic circuit of the microphone unit 20. The rear end of the microphone unit 20 is inserted into one end (front end) of the cavity sleeve 200 and thus the microphone unit 20 is supported by the cavity sleeve 200. While the plug assembly 30 is normally attached to the cavity sleeve 200, it is inserted/extracted into/from a grip housing 10 together with the cavity sleeve 200 at the one end of the grip housing 10, at which the microphone unit 20 is supported, for assembling or replacing the dynamic microphone. In this embodiment of dynamic microphone, while the inside of the cavity sleeve 200 functions as an air room, the inside of the grip housing does not entirely function as the air room, limiting the capacity of the air room.
In a still another embodiment of the dynamic microphone having an air room in a grip housing, a connector attachment of the grip housing has a slope, and an elastomer ring is attached to a connector. In this dynamic microphone, the elastomer ring is urged to the slope after assembling of the microphone, so that the inside of the grip housing is sealed. In such a dynamic microphone, the plug assembly is also inserted/extracted into/from the grip housing at the one end thereof, at which the microphone unit is supported, for assembling or replacing the dynamic microphone.